Movers and fakers ... The Faun made by Shaun Greenhalgh. Photograph: The Art Institute of Chicago/AP

If only the Art Institute of Chicago had put their prized possession into a cupboard and left it there for 50 years, they'd have seen it plain. "Aha," somebody would have remarked when it finally came out of its cupboard, "that little Bob Geldof dribble of a beard, those furry trousers - must be about 2007 ... fine thing, excellent workmanship."

It seems certain that the fake Gauguin, so brilliantly traced by the Art Newspaper from a garden shed in Bolton to one of the most prestigious museum in the US, will turn out to be in good company. Exposure is rarely as public and dramatic as the Gauguin, or the whole exhibition of terracotta warriors in Germany, which turn out to have gone awol not from Xi'an in China but from some much more recent workshop. But it also seems certain that more works by the remarkable Greenhalgh family, master fakers in a long tradition which has its own passionate admirers and collectors, are slumbering quietly in museum and private collections.

Time tends to date them remarkably precisely, like the newly restored 50-year-old print of the Hammer Dracula, which now looks as 1950s as I Love Lucy. Instead of this week's public disgrace, they usually simply disappear quietly off display and into the discreet darkness of the furthest corner of a museum store.

But in their day the best fakes can be extraordinarily convincing. Even though the techniques of paper, timber, canvas and pigment analysis were in their infancy, with the benefit of piercing hindsight it seems amazing that the fake Vermeers of the extraordinary Han van Meegeren weren't clocked immediately. In the 1930s and 40s his work, which now looks so clay-footed compared to the pale, luminous pigments of the real thing, seemed so plausible that he once faced execution as a collaborator for selling a genuine Vermeer to the Nazis. His explanation that the picture was a fake, and he was the faker, was completely disbelieved. He had to knock out another Vermeer, Jesus Among the Doctors, in prison, under heavy guard, to prove it.

Like Shaun Greenhalgh, who never managed to get into art school, and carried a chip on his shoulder over rejection by an art world which he never seems seriously to have tried to penetrate, and Tom Keating, a Cockney who could turn his hand to any style and whose fakes now sell better than many of his contemporaries, Van Meegeren said his forgeries were "spurred by the disappointment of receiving no acknowledgements from artists and critics" for his own work.

Fakers may end up doing it for the money - and John Myatt, once locked up in Brixton nick for forgery, now earns a healthy living turning out signed, acknowledged fakes - but that's rarely where it begins. Michelangelo created a Roman cupid, aged by burying in a dunghill, in a contemptuous effort to see if the patrons snubbing him would buy his work if they thought it had 2,000 years of pedigree.

The British Museum's 1980s exhibition on Fakes included a mermaid, a unicorn's horn, and a whole case of Billy and Charley's (Greenhalghs of 19th-century London, brilliant forgers whose east London 19th-century workshop could turn out anything from a bronze age dagger to a medieval ring) was one of its most popular ever.

I hope some museum is already negotiating through the bars with Shaun Greenhalgh, and lining up his parents who, in their 80s, helped create utterly plausible paper trails for his work, with a view to a major exhibition on his release. He will, after all, have plenty of time on his hands in the next few years. If there's room to spare they should try and borrow the terracotta imposters too: it could be a sensation.